multifoil insulation ??

[DIYedboy]

Is the consensus that these things are useless? I believe that there's no substitute for thickness but I'm no expert like some of you????

 

[freddiemercurystwin]

It only works when used in conjunction with other rigid insulation such as celotex and air cavities either side of it meaning any space-saving advantage is lost. And not cheap either. In short you don't gain anything by using it.

 

[cjard]

Pretty much, yeah. There are alternatives to thickness - vacuums for example - but they're so outrageously expensive compared to regular kingspan that you really only want them if you have some awkward detail that needs the slenderness and cannot be adjusted to use thicker insulation. Once you've got a wall U value of around 0.15 you're better off throwing your thousands at getting better air tightness to stop draughts than you are trying to get the wall down to a theoretical 0.1 etc. That's probably where multifoils get their ability to claim performance in the field from - they insist on meticulous taping and jointing which, when done properly, will vastly improve the air tightness of the dwelling and reduce draughts.. So while these things may perform poorly in a hot box, in real world examples they seem to perform well because they're preventing heat loss via other means. And if they aren't then the manufacturers can always claim "it's a bad install" (and it probably will be, if installed by your typical builder)

 

[DIYedboy]

That's sorted then, no point using it unless there is an unusual problem to overcome................pity all the poor buggers that opted for it when it first came out!